Friday, October 23, 2015

If you've been keeping up with this blog then you understand a bit about IOMMU groups and device isolation. In my howto series I describe the limitations of the Xeon E3 processor that I use in my example system and recommend Xeon E5 or higher processors to provide the best case device isolation for those looking to build a system. Well, thanks to the vfio-users mailing list, it has come to my attention that there are in fact Core i7 processors with PCIe Access Control Services (ACS) support on the processor root ports.Intel lists these processors as High End Desktop Processors, they include Socket 2011-v3 Haswell E processors, Socket 2011Ivy Bridge E processors, and Socket 2011Sandy Bridge E processors. The linked datasheets for each family clearly lists ACS register capabilities. Current listings for these processors include:Haswell-E (LGA2011-v3)i7-5960X (8-core, 3/3.5GHz)i7-5930K (6-core, 3.2/3.8GHz)i7-5820K (6-core, 3.3/3.6GHz)Ivy Bridge-E (LGA2011)i7-4960X (6-core, 3.6/4GHz)i7-4930K (6-core, 3.4/3.6GHz)i7-4820K (4-core, 3.7/3.9GHz)Sandy Bridge-E (LGA2011)i7-3960X (6-core, 3.3/3.9GHz)i7-3970X (6-core, 3.5/4GHz)i7-3930K (6-core, 3.2/3.8GHz)i7-3820 (4-core, 3.6/3.8GHz)

These also appear to be the only Intel Core processors compatible with Socket 2011 and 2011-v3 found on X79 and X99 motherboards, so basing your platform around these chipsets will hopefully lead to success. My recommendation is based only on published specs, not first hand experience though, so your mileage may vary.Unfortunately there are not yet any Skylake based "High End Desktop Processors" and from what we've seen on the mailing list, Skylake does not implement ACS on processor root ports, nor do we have quirks to enable isolation on the Z170 PCH root ports (which include a read-only ACS capability, effectively confirming lack of isolation), and integrated I/O devices on the motherboard exhibit poor grouping with system management components (aside from the onboard I219 LOM, which we do have quirked). This makes the currently available Skylake platforms a really bad choice for doing device assignment.Based on this new data, I'll revise my recommendation for Intel platforms to include Xeon E5 and higher processors or Core i7 High End Desktop Processors (as listed by Intel). Of course there are combinations where regular Core i5, i7 and Xeon E3 processors will work well, we simply need to be aware of their limitations and factor that into our system design.EDIT (Oct 30 04:18 UTC 2015): A more subtle feature also found in these E series processors is support for IOMMU super pages. The datasheets for the E5 Xeons and these High End Desktop Processors indicate support for 2MB and 1GB IOMMU pages while the standard Core i5 and i7 only support 4KB pages. This means less space wasted for the IOMMU page tables, more efficient table walks by the hardware, and less thrashing of the I/O TLB under I/O load resulting in I/O stalls. Will you notice it? Maybe. VFIO will take advantage of IOMMU super pages any time we find a sufficiently sized range of contiguous pages. To help insure this happens, make use of hugepages in the VM.EDIT (Oct 15 18:20 UTC 2016): Intel Broadwell-E processors have been out for some time and as we'd expect, the datasheets do indicate that ACS is supported. So add to the list above:Broadwell-E (LGA2011-v3)i7-6950X (10-core, 3.0/3.5GHz)i7-6900K (8-core, 3.2/3.7GHz)i7-6850K (6-core, 3.6/3.8GHz)i7-6800K (6-core, 3.4/3.6GHz)